Liquid developers usually consist of developer particles suspended in an insulating liquid having a resistivity in excews of 10.sup.10 ohm. c.m. and a dielectric constant less than 3, the developer particles being coated with an insulating medium such as a resin whereby to control the polarity of the particles in the insulating liquid and also to provide the means whereby the rate of exchange of charges between the particles and a surface containing a latent electrostatic image is slowed down, and such resin or other insulating medium can also be such that on the position an evaporation of a carrier liquid this forms a fixing medium for the particles.
Such a developer is already well-known and various applications by the applicant have proceeded to the grant of patents and have been brought into commercial use.
One of the problems associated with developers of this type is that the particles tend to settle out, this settling increasing with a coarseness of the particles and thus it has been customary to prepare the developer in the form of a relatively thick paste and to break down the developer by adding the carrier liquid just prior to use on the developer, the paste being thoroughly mixed into the carrier liquid so that at the time of development the particles of toner or developer medium are uniformly dispersed throughout the carrier liquid.
It has been shown in the past that improved development results where there is agitation of the developer just prior to it being applied and also that improved images result where the developer is agitated at the time of application to the surface containing the latent electrostatic image, and to achieve this it has been proposed to apply the developer liquid to the surface with a washing action so that the surface is swept by the developer for a required time to ensure that sufficient particles are brought into the image field to deposit to give an image of a required density.